Feeding beef cattle cull onions

Oregon is a domestic leader in storage onion production and Malheur and Morrow counties lead production within the state. Historically, onion producers have experienced difficulties disposing of cull onions, which are damaged onions that cannot be sold for human consumption. They are problematic because they attract an onion maggot fly that results in economic losses. For this reason, several strategies have been proposed to mitigate economic losses and negative environmental impacts. One of the strategies was to feed cull onions to beef cattle. The practice reduced disposal costs to onion producers and decreased the cost of feed for Oregon beef cattle producers by lowering annual feed costs. What follows is a brief reflection on feeding cull onions as an alternative byproduct feedstuff with the intent to empower producers to identify the nutritional value of cull onions and how to feed them to beef cattle.

Nutritional Value

Cull onions have a nutritional value comparable to that of barley when compared on a dry matter basis. However, unlike barley, cull onions are mainly water with approximately 90% moisture (Table 1). Crude protein ranges from 9-13% on a dry matter basis with 70% of that identified as soluble protein. Cull onions are also highly digestible. The low fiber and lignin content contribute to the high total digestible nutrient (TDN) content that ranges between 83-90%. However, despite the good nutritive value, there are challenges associated with feeding cull onions to cattle.

Onion Poisoning

Beef producers near onion producing regions in Oregon have experienced setbacks feeding cull onions in beef cattle diets. One problem is that the cull onions can induce onion poisoning—also called beef toxicosis. Beef cattle have an affinity for cull onions and can acquire acute and potentially lethal disease if it becomes a large portion of their diet. In one instance, a beef cattle producer hauled just over one ton of cull onions in a pasture with 85 calves and yearlings that previously had access to low-quality grass silage. Signs of beef toxicosis were observed after five days, which affected 22 cattle with one fatality (Verhoeff et al 1985). These signs include a lack of appetite, taggering, yellow-colored eyes, and an increased heart rate. If these signs are apparent, restrict the access to onions. Too much cull onions in the diet leads to haemolytic anemia and acute death.

Mechanism of Action

The allium family, which includes garlic, shallots, and onions, contains unique compounds that induce beef toxicosis. These compounds have been identified as npropyldisulfide as well as two rare amino acids—S-meth- and S-prop(en)ylcystein sulfoxide (SMCO). In brief, microbes in the rumen convert SMCO from the diet into the intermediary, thiosulfonate, which is then converted into either dipropyl disulfides and/or dipropenyl disulfides. These disulfides, in addition to n-propyl disulfide, disrupt the normal oxygen binding capacity of hemoglobin in red blood cells by oxidizing Fe2+ to Fe3+. The change converts hemoglobin to methemoglobin, a molecule that does not bind oxygen and thereby leads to anoxia. Additionally, these disulfide compounds weaken normal red blood cell activity and promote the formation and precipitation of Heinz bodies within the cells. Cells with these formations are removed from circulation and results in anemia. These negative effects originally contributed to recommendations to abstain from feeding cull onions to beef cattle, which have since been reevaluated.

Feeding Cull Onions

Feeding cull onions has several limitations that should be considered by beef cattle producers—the cost and the quantity to feed. The primary limitation in feeding cull onions is the cost to transport the product. Cull onions are 90% water so it is important to calculate whether the cost for the 10% dry matter is feasible for the operation. Another limitation is how much cull onion to feed without compromising the growth and production of the herd. A 119-day feeding study conducted in 1992 highlighted the effects of increasing onion percentages in a ration of 36 calves weighing 529 pounds (Lincoln et al. 1992). The researchers reported the impacts on average daily gain, feed intake, and feed to gain ratio. Cattle performed well on a barley, corn silage, and alfalfa ration that contained nearly 25% cull onions on a dry matter basis (Table 2). None of the animals in the study acquired clinical anemia, which suggests the percentage is safe to feed.

Prevention Measures

Feeding cull onions can be an affordable option to mitigate high feed costs, however it has risks when not properly managed. Therefore, it is important to have the following prevention measures in mind:

Gradually increase cull onions in the diet to allow rumen microbes to adapt to the new diet.

Do not provide cull onions as a sole feedstuff.

Be attentive to the clinical signs of beef toxicosis and remove cull onions from the diet if there are any symptoms.

Chop and blend cull onions when feeding as an ingredient in a ration to prevent cattle from being too selective.

Conclusion

Successful beef cattle producers identify, acquire, and effectively use alternative feedstuffs in their regions to remain competitively nationwide. Cull onions are an option that some beef cattle producers in Oregon have utilized for years and can continue to utilize to remain as economically viable operations.

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